1. Field of the Invention
The present invention relates to a conductor structure and a method of forming the same. More particularly, the present invention relates to a conductor structure for a display or an electro-optical device and a method of forming the same.
2. Descriptions of the Related Art
With evolving manufacturing technologies, the liquid crystal display (LCD) has demonstrated its advantage over other displays in terms of image compactness, power consumption and service life. As a result, LCDs have been replacing conventional image tube displays. However, with the increase in the size and resolution of the thin film transistor-LCD (TFT-LCD) panels, the RC delay of signal transmissions within metal conductors has increased. In this case, reducing the RC delay has become difficult.
Since the speed of a signal transmission within a conductor is determined by the product of the resistance (R) and the capacitance (C) of the conductor, the common solution to reduce the RC delay is using a metal with a low resistivity, such as Al or even Cu. For example, Al conductors have a resistivity of about 5 μΩ/cm, while that of copper conductors may have a resistivity as low as 2.2 μΩ/cm. Hence, if copper conductors are adopted, the resistance value thereof will be decreased significantly, thus eliminating the image delay even for an increased panel size. Furthermore, the cost of the material will become less expensive than those adopted in the current mass production technology.
A conventional process for manufacturing copper conductors is described briefly: a barrier layer 11 and a copper layer 13 is first formed on a glass substrate 10, as shown in FIG. 1A. Then a photoresist layer 15 is formed on the glass substrate 10 and is patterned, as shown in FIG. 1B. Subsequently, an etching process is performed to remove portions of the barrier layer 11 and the copper layer 13 are not covered by the photoresist layer, as shown in FIG. 1C. Finally, the photoresist layer 15 is removed to complete the copper conductor manufacturing process, as shown in FIG. 1D. However, in the conventional process for manufacturing copper conductors in an LCD, a number of difficulties have been encountered. For example, it is difficult to etch copper into a predetermined structure. When a copper conductor is manufactured, it is impossible to etch the metal with the same etchant solution used in conventional manufacturing processes (e.g. an Al etchant solution). As a result, new etchant solutions have to be developed, which is very time consuming and labor intensive. Furthermore, the etchant solutions used for copper have a short life-time, leave residuals in the copper/barrier layer and render the taper structure is not good. In addition, the copper element used for forming the conductor structure is prone to diffuse into both the dielectric layer and the semiconductor layer, which may cause a short circuit or electron migration, thus adversely affecting the production yield significantly.
It can be seen from the above description that it is difficult to pattern the copper layer during the conventional manufacturing process. In view of this, it is important to provide a method for forming a copper conductor structure that can overcome these difficulties.